Drop shock measurement system and acceleration sensor element used in the same

ABSTRACT

The drop impact measuring system has i) a plurality of bimorph-type acceleration sensor containing a plurality of free vibrating sections each of which has individual draw-out electrodes; ii) a switch section for selecting output from the bimorph-type acceleration sensors; iii) an amplifying circuit for amplifying a signal applied via the switch section from the acceleration sensors; and iv) a logic circuit for logically evaluating the output from the amplifying circuit and controlling the switch section according to the result acquired from the logical evaluation.

This application is a continuation in part of U.S. patent applicationSer. No. 10/769,263, filed Jan. 30, 2004 which is a divisional of U.S.patent application Ser. No. 10/398,138, filed Aug. 14, 2003 nowabandoned, which is a U.S. National Phase Application of PCTInternational Application PCT/JP02/08053 the contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a drop impact measuring system used fora drop impact test on mobile electronic equipment including a mobilephone, and also relates to an acceleration sensor element employed forthe drop impact measuring system.

BACKGROUND ART

For mobile electronic equipment including a mobile phone, a notebooksize computer, a mobile cassette player, compact disc (CD) player, andmini disc (MD) player, dropping of the equipment is an ever-presentdanger when considering its intended use. Accordingly, protecting theequipment from impact caused by dropping the equipment has now been agrowing need. A typical failure comes from distortion of a motherboardmounted on the equipment due to drop impact, by which some on-boardcomponents have shorts in the wiring, or come off the board. Therefore,to protect the equipment from such accidents, the following steps shouldbe taken: i) selecting a material and a structure of electronicequipment to be tested; ii) determining a drop height and direction;iii) simulating drop impact acceleration applied to each section of theequipment; and then iv) getting feedback from the result and improvingthe design of the inner structure, for example, the position and methodof installing a circuit board. However, the drop impact accelerationduring falling greatly varies between different falling objects, and theacceleration applied to an object has significant consequence to theimpact force. Furthermore, mechanical vibration and its correspondingfrequency caused by the drop impact greatly depends on the structure ofan object. The reasons above have been obstacles to detecting dropimpact acceleration applied to a falling object.

DISCLOSURE OF THE INVENTION

The drop impact measuring system has i) a plurality of bimorph-typeacceleration sensors containing a plurality of free vibrating sectionseach of which has individual draw-out electrodes; ii) a switch sectionfor selecting output of the bimorph acceleration sensors obtainedthrough the draw-out electrodes; iii) an amplifying circuit foramplifying at least one of voltage and current applied via the switchsection from the bimorph acceleration sensors; and iv) a logic circuitfor logically evaluating the output from the amplifying circuit andcontrolling the switch section according to the result acquired from thelogical evaluation.

A bimorph acceleration sensor element is formed of the free vibratingsections having cantilever beams. Signals generated at the freevibrating section are fed through the draw-out electrodes to the switchsection.

The bimorph acceleration sensor element is also formed of the freevibrating section having both-ends-supported beams. Signals generated atthe free vibrating section are fed through the draw-out electrodes tothe switch section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a circuit diagram of a drop impact measuring system inaccordance with a first and a second embodiments of the presentinvention.

FIG. 2A shows a circuit diagram of an acceleration sensor of the firstembodiment.

FIG. 2B shows a circuit diagram of an acceleration sensor of the secondembodiment.

FIG. 3 is a flow chart illustrating the routine of detecting drop impactacceleration in a drop impact measuring system of the first and secondembodiments.

FIG. 4 is another flow chart illustrating the routine of detecting dropimpact acceleration in a drop impact measuring system of the first andsecond embodiments.

FIG. 5A shows a top view of an acceleration sensor element having aboth-ends-supported beam structure in accordance with the firstembodiment.

FIG. 5B shows a bottom view of the acceleration sensor element having aboth-ends-supported beam structure in accordance with the firstembodiment.

FIG. 5C shows a side view of the acceleration sensor element having aboth-ends-supported beam structure in accordance with the firstembodiment.

FIG. 5D shows a perspective view of the acceleration sensor elementhaving a both-ends-supported beam structure in accordance with the firstembodiment.

FIG. 6A shows a top view of an acceleration sensor element having acantilever beam structure in accordance with the second embodiment.

FIG. 6B shows a bottom view of the acceleration sensor element having acantilever beam structure in accordance with the second embodiment.

FIG. 6C shows a perspective view of the acceleration sensor elementhaving a cantilever beam structure in accordance with the secondembodiment.

FIG. 7A shows a top view of an acceleration sensor element having acantilever beam structure in accordance with the first embodiment.

FIG. 7B shows a bottom view of the acceleration sensor element having acantilever beam structure in accordance with the first embodiment.

FIG. 7C shows a perspective view of the acceleration sensor elementhaving a cantilever beam structure in accordance with the firstembodiment.

FIG. 8A shows a top view of another acceleration sensor element having acantilever beam structure in accordance with the first embodiment.

FIG. 8B shows a bottom view of the acceleration sensor element having acantilever beam structure in accordance with the first embodiment.

FIG. 8C shows a perspective view of the acceleration sensor elementhaving a cantilever beam structure in accordance with the firstembodiment.

BEST MODE FOR CARRYING OUT OF THE INVENTION First Exemplary Embodiment

The present invention relates to method and apparatus which is used inthe development of electronic equipment. It is known that electronicequipment (e.g. consumer electronics) is prone to damage when exposed tophysical shock. Such physical shock may occur, for example, when theelectronic equipment is accidentally dropped on a hard surface. Thus, itis desirable to design and build electronic equipment in a manner sothat it can receive as much physical shock as possible and stillcontinue to operate. As discussed in the “Background of the Invention,”exposing electronic equipment to physical shock can cause the equipmentto malfunction by distorting the equipment's motherboard or causingshorts in the wiring.

Thus, during the design phase of electronic equipment, it is desirableto place some sort of sensor and then to drop the equipment (with thesensor in place). The sensor can provide an indication of the amount ofphysical shock sustained by the equipment as a result of, for example,being dropped. Based on the information provided by the sensor, thephysical design of the equipment can then be modified in order todecrease the effects of physical shock.

One problem with this approach is determining what type of sensor toplace in the equipment for this type of testing. For this purpose, anacceleration sensor element may be used. It is desirable, however, toselect an acceleration sensor which, when dropped with the electronicequipment being tested, does not have its vibration frequency bandwidththreshold exceeded. In accordance with the present invention, a methodand apparatus are provided to test electronic equipment with variousfree vibrating sections until a free vibrating section is identifiedwhich does not exceed its vibration frequency bandwidth when exposed tophysical shock. Having selected that free vibrating section, that freevibrating section in an acceleration sensor as development of theelectronic equipment continues.

FIG. 1 shows a circuit diagram of a drop impact measuring system inaccordance with a first embodiment of the present invention.Acceleration sensors 101, 102, and 103 are connected to switches 106,107, and 108, respectively. Sensors 101 through 103 are also connectedto ground 109. By closing one of switches 106 through 108, an outputsignal from one of acceleration sensors 101 through 103 is fed intoamplifying circuit 104 to be amplified. Amplifying circuit 104 outputs asignal, which corresponds to acceleration, via terminal 110. Logiccircuit 105 evaluates whether or not the signal from amplifying circuit104 stays within a predetermined frequency threshold and whetherresonance occurs or not, and then accordingly outputs logicallyevaluated result. Logic circuit 105 determines which one of switches 106through 108 should be closed, according to the logical evaluation,thereby controlling switches 106 through 108.

FIGS. 5A through 5D show the structure of an acceleration sensorelement, which is the major component of acceleration sensors 101through 103. FIGS. 5A through 5D shows an acceleration sensor elementhaving a both-ends-supported beam structure. FIG. 5A is a top view; FIG.5B is a bottom view; FIG. 5C is a side view; and FIG. 5D is aperspective view. Each of free vibrating sections 545 through 547 shownin FIGS. 5A through 5D has a bimorph structure in which distortion andmechanical vibration occurs when an impact force is applied. Freevibrating sections 545, 546, and 547 have main electrodes 501, 502, and503 on each upper surface thereof, and have main electrodes 520, 521,and 522 on each lower surface thereof, respectively. Draw-out electrodes504 and 505 are connected with main electrode 501; draw-out electrodes506 and 507 are connected with main electrode 502; and draw-outelectrodes 508 and 509 are connected with main electrode 503 toestablish electrical connections, respectively. Free vibrating sections545 through 547 generate electric charges according to distortion inshape due to their bimorph structures. The electric charge generated oneach upper surface of free vibrating sections 545, 546, and 547 iscarried to main electrodes 501, 502, and 503, respectively, and furthercarried to draw-out electrodes 504 and 505; 506 and 507; 508 and 509,respectively. On the other hand, the electric charge generated on eachlower surface of free vibrating sections 545, 546, and 547 is carried tomain electrodes 520, 521, and 522, respectively, and further carried todraw-out electrodes 523 and 524; 525 and 526; 527 and 528, respectively.The electric charges carried to main electrodes 520 through 522 areopposite in polarity to those carried to main electrodes 501 through503. Draw-out electrodes 523 through 528 are extended to the bottom ofsupporters 541 through 544, via the side surfaces of the supporters, andare exposed at the bottom of the each supporter.

The deformation of free vibrating sections 545 through 547 createsoppositely polarized electric charges: one is drawn out by draw-outelectrodes 504 through 509 disposed on the upper surface of freevibrating sections 545 through 547; the other is drawn out by draw-outelectrodes 523 through 528 exposed at the bottom of supporters 541through 544.

The reason why draw-out electrodes 504 through 509 and 523 through 528are formed as a part of free vibrating sections 545 through 547 is asfollows: such a structure can avoid cancellation of the drawn outelectric charge due to stress distribution in free vibrating sections545 through 547. in the structure above, for example, each width ofdraw-out electrodes 504 and 505 is determined less than one-fifth ofthat of main electrode 501.

Free vibrating sections 545, 546, and 547 have lengths of L3, L2, andL1, respectively, and in which L3 is the longest, and L1 is theshortest. Free vibrating sections 545 through 547 are electricallyseparated each other.

FIG. 2A shows the circuit diagram of acceleration sensors 101 through103 shown in FIG. 1. Acceleration sensor element 201 is the one the sameas shown in FIGS. 5A through 5D. One of draw-out electrodes 523 and 524shown in FIGS. 5A through 5D is connected to ground 205 of FIG. 2A. Onthe other hand, one of draw-out electrodes 504 and 505 shown in FIGS. 5Athrough 5D is connected to resistor 202 of FIG. 2A. The electric chargeobtained from draw-out electrode 504 or 505 is converted throughresistor 202 into current. Besides, feeding the current through resistor202 allows resistor 202 to generate voltage. In the case that resistor202 is required to have large resistance value more than 1 MΩ, employingfield-effect transistor (FET) 203 allows the circuit to have lowerimpedance. The source of FET 203 is connected, through terminal 206, tothe positive side of a power-supplying unit; the gate is connected tothe acceleration sensor element 201 and resistor 202; and the drain isconnected to resistor 204. The other terminal of resistor 204 isconnected to ground 205. The potential of the drain is taken out throughterminal 207. Forming the circuit like this allows terminal 207 to havelower output impedance.

The acceleration sensor element shown in FIGS. 5A through 5D also hasfree vibrating sections 546 and 547. Each signal obtained from the twosections is similarly processed, as shown in FIG. 2A.

A signal from terminal 207 is fed to the corresponding one of switches106 through 108.

In the embodiment, ID numbers 1 through 3 are assigned to theacceleration sensors having free vibrating sections 545 through 547,respectively, and a letter “S” indicates the ID number: S=1 inacceleration sensor 101 containing free vibrating section 545; S=2 inacceleration sensor 102 containing free vibrating section 546; and S=3in acceleration sensor 103 containing free vibrating section 547.Similarly, a letter “N” represents the total number of accelerationsensors: N=3 in the acceleration sensors shown in FIGS. 5A through 5D.

Although the explanation above introduces the structure in which i)generating current by moving the electric charge obtained from one ofdraw-out electrodes 504 and 505; ii) converting the current into voltageby feeding through resistor 202; and then iii) amplifying the voltage,it is not limited thereto: the structure in which current is directlyamplified is also acceptable.

Acceleration sensor element 201 generally bears capacitance—working thecapacitance with resistor 202 inevitably forms a filter that cuts offlow band frequencies. Therefore, the signals generated in accelerationsensor element 201 have decreased low band frequencies. In this case,the low-band cut-off frequency, “Fc” is given by the expression below.Fc=1/(2π×R×Cs)  (Expression. 1),where, Cs represents capacitance of acceleration sensor element 201; Rrepresents resistance of resistor 202.

FIG. 3 is a flow chart illustrating the routine of measuring drop impactin the circuit shown in FIG. 1. The purpose of this routine is toidentify the free vibrating section most suitable for measuring dropimpact for electronic equipment having a drop impact detection device.In the first step 300, an acceleration sensor including the freevibrating section that measures the lowest mechanical vibrationfrequency bandwidth is selected from free vibrating sections 545 through547 of different lengths as shown in FIGS. 5A through 5D; accelerationsensor 101 including free vibrating section 545 measures the lowestmechanical vibration frequency bandwidth, that is, “S” takes on 1.

In step 301, among switches 106 through 108, only one switch associatedwith the acceleration sensor selected in step 300 is closed, wherebysensor switching is performed. At the moment, since “S” retains thevalue of 1, only switch 106 of FIG. 1 is closed.

In step 302, the drop down test begins.

In step 303, drop impact is measured. Amplifying circuit 104 amplifiessignals from acceleration sensor 101 generated by the drop impact andthen outputs the measured result (i.e., impact acceleration) throughterminal 110 shown in FIG. 1.

In step 304, logic circuit 105 evaluates whether the output signal fromamplifying circuit 104 stays within a vibration frequency bandwidththreshold or not, and whether resonance occurs or not.

In step 306, if the impact acceleration stays within the vibrationfrequency bandwidth threshold, the acceleration is displayed in step312. A display for showing the impact acceleration is not shown in FIG.1.

On the other hand, if the impact acceleration exceeds the vibrationfrequency bandwidth threshold, the procedure goes to step 307. In step307, the value currently stored in S is compared with the value storedin N.

If the comparison finds that the value of S equals to that of N—whichmeans that each of the output signals generated from free vibratingsections 545 through 547, shown in FIGS. 5A through 5D, via amplifyingcircuit 104 exceeds the vibration frequency bandwidth threshold in eachof the free vibrating sections, the procedure goes to step 311, where anerror indication is shown on the display.

On the other hand, if S does not reach N, the procedure goes to step 310where the value of S (that indicates a sensor number) is updated. Thatis, S is incremented by 1 in step 310, and then the procedure goes backto step 301. According to the updated S, next acceleration sensor isselected in step 301, and the drop impact measurement is resumed fromstep 302.

FIG. 4 is another flow chart illustrating the routine of measuring dropimpact in the circuit shown in FIG. 1. According to the flow chart shownin FIG. 3, if the result of the drop impact measurement obtained at step303 exceeds the vibration frequency bandwidth threshold of Srepresenting a sensor number, the value of S is incremented by 1 in step310, and then the drop-impact measurement is resumed at step 302. On theother hand, in the flow chart of FIG. 4, even if the first result of themeasurement exceeds the vibration frequency bandwidth threshold of S,the logic circuit evaluates output signals to find a proper sensornumber, and then the drop impact measurement is resumed with theacceleration sensor corresponding to the sensor number.

In step 400, S initially takes on 1, and the drop impact test begins atstep 401. Next, in step 402, amplifying circuit 104 amplifies the outputsignal of acceleration sensor 101 that has been entered through switch106.

In step 403, logic circuit 105 evaluates whether the output signal fromamplifying circuit 104 stays within a vibration frequency bandwidththreshold or not, and whether resonance occurs or not.

In step 404, if the logic circuit evaluates that the impact accelerationstays within a vibration frequency bandwidth threshold, the accelerationis displayed in step 408. A display for showing the impact accelerationis not shown in FIG. 1.

On the other hand, if the impact acceleration exceeds the vibrationfrequency bandwidth threshold of the current sensor, logic circuit 105selects a proper sensor number according to the output signal ofamplifying circuit 104 in step 406.

In step 407, a switch corresponding to the sensor number selected aboveis closed to resume the drop impact test.

In step 408, the drop impact is measured and displayed.

An acceleration sensor for detecting drop impact is required to havedifferently ranged vibration frequency bandwidths, that is, desirably tohave various frequencies, not only one.

In the acceleration sensor element shown in FIGS. 5A through 5D, supposethat “fr” represents the resonance frequency; “L” represents the lengthof the free vibrating section; “t” represents the thickness; and “α”represents a constant, “fr” is given by the expression below:Fr∝α×T/L²  (Expression 2).

That is, the resonance frequency “fr” varies inversely with the squareof the length of the free vibrating section. The acceleration sensorelement shown in FIGS. 5A through 5D has free vibrating sections 545through 547 of different lengths, thereby offering various vibrationfrequency bandwidths. The acceleration sensor element shown in FIGS. 5Athrough 5D is thus ready to detect various resonance frequencies withineach of the free vibrating section bandwidths.

Employing such structured acceleration sensor element for a drop impactmeasuring system can easily detect impact acceleration, even in the casethat a mechanical vibration frequency at the drop down of an object isunpredictable in advance. Accordingly, it will contribute to easystructural design of the housing.

Each of FIGS. 7A through 7C, and FIGS. 8A through 8D shows anacceleration sensor element having a cantilever beam structure.

FIG. 7A is a top view, FIG. 7B is a side view, and FIG. 7C is aperspective view. The structure in which supporter 744 holds each oneend of free vibrating sections 741 through 743 forms into a cantileverbeam. Free vibrating sections 741, 742, and 743 have main electrodes701, 702, and 703 on the upper surfaces thereof, and main electrodes721, 722, and 723 on the lower surfaces thereof, respectively. Draw-outelectrodes 724, 725, and 726, which are formed on the bottom ofsupporter 744, are electrically connected with main electrodes 721, 722,and 723, respectively.

Each of FIGS. 8A through 8D shows another acceleration sensor elementhaving the cantilever beam structure. FIG. 8A is a top view, FIG. 8B isa bottom view, and FIG. 8C is a perspective view. The structure in whichsupporter 843 holds each one end of free vibrating sections 841 and 842forms into a cantilever beam. Free vibrating section 841 has mainelectrode 801 on the upper surface thereof, and main electrode 821 onthe lower surface thereof. Similarly, free vibrating section 842 hasmain electrode 802 on the upper surface thereof, and main electrode 822on the lower surface thereof. Draw-out electrodes 803 and 804 areelectrically connected with main electrodes 801 and 802, respectively.Draw-out electrode 823, which is formed on the bottom of supporter 843,runs across side 844 of the supporter and reaches main electrode 821 tohave electric connections. Similarly, draw-out electrode 824, which isalso formed on the bottom of supporter 843, runs across the sideopposite to side 844 of the supporter and reaches main electrode 822 tohave electric connections.

When comparisons are made between the acceleration sensor element formedinto a cantilever beam structure shown in FIGS. 7A through 7C and FIGS.8A through 8C; and the acceleration sensor element formed into a bothends-supported beam structure shown in FIGS. 5A through 5D, thecantilever beam structure generates four to five times more amount ofoutput electrical charge than the both ends-supported beam structuredoes, provided they have same dimensions. Therefore, amplifying circuit104 of FIG. 1, which is necessary for the acceleration sensor elementhaving the both ends-supported beam shown in FIGS. 5A through 5D, can beeliminated by using the cantilever beam structure. Eliminating theamplifying circuit can provide a low-cost drop impact measuring system.Besides, the parallel arrangement of free vibrating sections 741 through743 allows the whole structure of the acceleration sensor element to becompact, accordingly providing a downsized drop impact measuring system.

Employing the structure explained in the first embodiment can providethe drop impact measuring system that easily measures an impactacceleration of even more than 1000G having great variations inresonance frequency. At the same time, the structure of the embodimentalso provides an acceleration sensor element capable of detecting impactacceleration of various resonance frequencies.

Second Exemplary Embodiment

FIG. 1 also shows a circuit diagram of the drop impact measuring systemof the second embodiment. FIG. 2B shows a circuit diagram of theacceleration sensor of the second embodiment. FIGS. 3 and 4 are flowcharts illustrating the routine of detecting drop impact acceleration inthe drop impact measuring system of the second embodiment. Each of FIGS.6A through 6C shows an acceleration sensor element having a structure ofcantilever beam of the second embodiment.

FIG. 6A is a top view, FIG. 6B is a bottom view, and FIG. 6C is aperspective view. Each one end of free vibrating sections 641 through644 are supportably fixed by supporter 645. Free vibrating sections 641,642, 643, and 644 have main electrodes 601, 602, 603, and 604 on theupper surfaces thereof, and have main electrodes 620, 621, 622, and 623on the lower surfaces thereof, respectively. Main electrodes 601, 602,603, and 604 are electrically connected with draw-out electrodes 605,606, 607, and 608, respectively. Similarly, main electrodes 620, 621,622, and 623 are electrically connected with draw-out electrodes 624,625, 626, and 627, respectively. Draw-out electrodes 624 through 627 areexposed from the bottom of supporter 645. Free vibrating sections 641,642, 643, and 644 are of the same length, which are represented by L4,L5, L6, and L7, respectively.

Using the acceleration sensor element shown in FIGS. 6A through 6C, theacceleration sensor is formed, as shown in FIG. 2B. That is,acceleration sensor element 220 is formed of free vibrating section 641;main electrodes 601 and 620; and draw-out electrodes 605 and 624. Offour acceleration sensor elements shown in FIGS. 6A through 6C, one isused for sensor element 220; any one of the rest three is to be employedfor sensor element 221. Draw-out electrodes 624 through 627 areconnected to ground 225. On the other hand, draw-out electrodes 605through 608, which are electrically connected in parallel, and thenconnected to resistor 222. Resistors 222 and 224, FET223, terminals 226and 227 shown in FIG. 2B act the same as resistors 202 and 204, FET203,terminals 206 and 207 shown in FIG. 2A, respectively, therefore theexplanation of the components above will be omitted. Such structuredacceleration sensor serves as acceleration sensor 101 shown in FIG. 1.

Although acceleration sensors 102 and 103 are formed in the same mannerwith sensor 101, each acceleration sensor element used for these threesensors has a different frequency bandwidth range for mechanicalvibration. That is, the acceleration sensor can measure accelerationvalues in wide-ranged frequency bandwidth.

To measure greater drop impact acceleration, miniaturizing theacceleration sensor element and increasing mechanical strength seems tobe an effective way. According to a prior-art acceleration sensorelement, however, miniaturization of a sensor element has loweredelectric capacity and thereby degraded durability of noisecharacteristics of the sensor element itself Whereas the sensor elementintroduced in the second embodiment, by virtue of the structure in whichthe free vibrating sections of same resonance frequencies areelectrically connected in parallel, has no decrease in electric capacityif the sensor element itself is miniaturized. Therefore, the structuredescribed in the second embodiment can provide a high-noise-durabilityacceleration sensor element and a drop impact measuring system using thesensor element.

A prior-art acceleration sensor element, as described above, lowerselectric capacity as it is miniaturized. As a result, the “Fc” given bythe Expression 1, which represents low-band cut-off frequency, takes ona large value. Whereas the acceleration sensor element of the secondembodiment has no decrease in electric capacity, thereby keeping thelow-band cut-off frequency “Fc” from getting high.

Although the acceleration sensor of the second embodiment is formed ofthe acceleration sensor element having the shape illustrated in FIGS. 6Athrough 6C, it is not limited thereto: the similar effect can beobtained by the structure having free vibrating sections 741, 742, and743 (FIGS. 7A through 7C) of same lengths, i.e., L10=L9=L8; thestructure having free vibrating sections 841 and 842 (FIGS. 8A through8C) of same lengths, i.e., L11=L12; or the structure having freevibrating sections 545, 546, and 547 (FIGS. 5A through 5D) of samelengths, i.e., L3=L2=L1.

INDUSTRIAL APPLICABILITY

The drop impact measuring system and the acceleration sensor elementemployed for the system of the present invention can cope well with awide range of mechanical vibration frequencies and large impactaccelerations. Besides, the acceleration sensor element can beminiaturized and improved in durability of noise characteristics.

1. A drop impact measuring system for drop testing equipment, saidsystem comprising: a) a plurality of bimorph-type acceleration sensorsto be used for identifying one of a plurality of free vibrating sectionsincluded in each of said bimorph-type acceleration sensors,respectively, each of said free vibrating sections has a respectiveindividual draw-out electrode and respectively different bandwidth; b) aswitch section for allowing selection of one of the outputs of theplurality of bimorph-type acceleration sensors obtained through eachdraw-out electrode; c) an amplifying circuit for amplifying at least oneof voltage and current applied via the switch section from thebimorph-type acceleration sensors; and d) a logic circuit for performinga measurement of an output from the amplifying circuit when said dropimpact measuring system is dropped with the equipment and forcontrolling the switch section to change selection of the outputs of theplurality of bimorph-type acceleration sensors for a subsequentmeasurement according to a result of said measurements.